I. Field of the Invention
The present invention generally relates to intravascular devices for treating certain medical conditions and, more particularly, relates to intravascular occlusion devices for selective occlusion of a vessel, channel, lumen or cavity anywhere in the body's circulatory system where it is desired to stop the flow of blood. The devices made in accordance with the invention are particularly well suited for delivery through a small diameter flexible catheter or the like to a remote location treatment site in a patient's vascular system within a patient's body to occlude the site quickly by providing a high metal to volume ratio. The device can have a high ratio of delivery length to deployed length and can reach locations more tortuous than conventional occlusion devices.
II. Description of the Related Art
A wide variety of intravascular devices are used in various medical procedures. Certain intravascular devices, such as catheters and guidewires, are generally used simply to deliver fluids or other medical devices to specific locations within a patient's body, such as a selective site within the vascular system. Other, frequently more complex, devices are used in treating specific conditions, such as devices used in removing vascular occlusions or for treating vascular defects such as aneurysms and the like.
In certain circumstances, it may be necessary to occlude a patient's vessel, lumen, channel, hole or cavity such as to stop blood flow therethrough.
Mechanical embolization devices are well known in the art and sold commercially for occlusion of vessels in various locations within the vasculature. U.S. Pat. No. 6,123,715 by Amplatz and U.S. Pat. No. 5,725,552 by Kotula disclose intravascular occlusion devices fabricated from Nitinol braided metal fabric which are heat set in molds to an expanded shape, but which can be compressed for delivery through a catheter to a treatment site, whereby the device, when urged out of the delivery catheter, self expands within the vasculature to occlude blood flow at the treatment site. The details of the various designs and configurations as well as methods of fabricating and using the devices are detailed in the aforementioned patents and that are hereby incorporated in total herein by reference.
Although the occlusion devices described by Amplatz and Kotula patents are quite effective, there are significant improvements that can be made. In the Amplatz U.S. Pat. No. 5,725,552, there is shown, in FIGS. 5A and 5B, an elongated braided metal fabric vascular occlusion device which incorporates two spaced apart expanded diameter disk elements between the ends. The disk elements are intended to engage the vessel inside surface to cause thrombosis of the vessel by interaction of the blood and the Nitinol wire fabric. The disk elements are also sized in their freely expanded state to be somewhat larger in diameter than the vessel inside diameter to help anchor the device. This imparts a load from the Nitinol braid's desire to expand larger to be imparted against the wall defining a body lumen to secure the device in place.
The disks are preferably spaced apart to stabilize the device within the vessel and prevent the device from turning off axis to the vessel. The device is elongated for delivery through a catheter lumen by pulling the end wire clamps away from each other. This action draws the device diameter down for insertion into the catheter. A delivery system consisting of an elongated wire with a threaded end which engages a mating threaded end on one of the wire end clamps on the device allows the device to be pushed through the delivery catheter. As the device emerges out the distal end of the catheter, the device self-expands to its memorized pre-determined heat set shape. The treaded connection allows control of the device for retrieval, repositioning, or to be selectively released once the device is properly placed in the vessel.
The disk diameters in their relaxed state are somewhat larger in diameter than the delivery catheter lumen diameter. The stiffness of the disks and their large diameter contribute to the force required to push the device through delivery catheter. Additionally, since the device is being pushed from the proximal end rather than pulled from the distal end, the device is slightly compressed which leads to a small amount of outward expansion and also contributes to the delivery force required. To reduce this load, the lumen of the delivery catheter may have to be increased. However, this causes the delivery catheter to be stiffer and less able to easily pass through tortuous vessels than otherwise. Also the amount of metal density for a given volume occupied can affect the rate at which thrombosis will occur to occlude the vessel. Generally, the more metal exposed to the blood flow, the faster the thrombosis rate; also, more metal typically equates to a lower rate of device recanalization after implant. The Amplatz device has a relatively low metal to volume ratio compared to the inventive design described herein and therefore often uses added polyester fiber to enhance the thrombosis rate.
Another prior art occlusion device is described in U.S. Pat. No. 6,033,423 by Ken et. al “Multiple Layered Occlusive Coils”. This patent describes a vaso-occlusive device intended for occluding a vessel or an aneurysm, primarily in the brain. The occlusive device is a small diameter coiled wire, preferably 0.010-0.018 inch in diameter made preferably of a shape memory material such as Nitinol. The coiled wire is wrapped about itself and heat set to retain a three dimensional volume occupying shape to occlude a vessel. The coil is stretched to reduce its profile to that of the coil itself for introduction through a catheter. The coils are very flexible and can be passed through small diameter tortuous vessels, such as are encountered in the brain via a micro catheter. Because the coil diameter must be maintained small for passage through a small diameter catheter, the length of the coil to fill a given volume is quite long. The practicality of using such small coils in larger volumes, such as aneurysms found outside the neuro-vasculature or in a cavity of significant volume is reduced due to the small occupying volume of these micro coils.
Accordingly, it is advantageous to provide an improved vasculature occlusion device which offers better volume filling capability for a given length of implant, smaller delivery catheter diameter than conventional prior art systems, lower forces for advancement of the device through the delivery catheter, enhanced ability to traverse a tortuous vessel, and an increased rate of thrombosis by providing a higher metal to volume ratio.
In addition it would be advantageous in certain circumstances to be able to deliver the device using an “over the wire” approach, as well known in the angioplasty catheter field. It would also be beneficial to have a greater shape retention force by the addition of an optional shape retention wire to assist or provide the vessel occlusive device final shape.